linux-kernel - Re: [tip:perf/core] perf tools, Alpha: Add Alpha support to perf.h

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Date:	Tue, 10 Nov 2009 22:21:36 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	mingo@...hat.com, hpa@...or.com, paulus@...ba.org,
	linux-kernel@...r.kernel.org, ink@...assic.park.msu.ru,
	tglx@...utronix.de, rth@...ddle.net, mingo@...e.hu,
	mcree@...on.net.nz, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] perf tools, Alpha: Add Alpha support to perf.h

On Mon, 2009-10-26 at 14:08 +0200, Pekka Enberg wrote:
> > +#ifdef __alpha__
> > +#include "../../arch/alpha/include/asm/unistd.h"
> > +#define rmb()          asm volatile("mb" ::: "memory")
> > +#define cpu_relax()    asm volatile("" ::: "memory")
> > +#endif
> 
> OK, I'll bite. We tell userspace developers not to include kernel
> headers. Why is it okay for perf to do it (especially for something
> that's in asm)? 

The reason we take the explicit arch header is because we need the perf
syscall thingy, which isn't yet in the installed system unistd.h because
that's probably some ancient version.

Once distro's have had perf enabled kernels for long enough that all of
userspace has the syscall bits we can remove it.

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